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Megaloblastic Anemia
Macrocytic anemia caused by impaired DNA synthesis in red blood cell precursors, usually from vitamin B12 or folate deficiency.
Hallmark findings: MCV >100 fL, hypersegmented neutrophils, elevated methylmalonic acid (B12 deficiency) or homocysteine (both B12 and folate deficiency). Causes of B12 deficiency include pernicious anemia, ileal disease, gastric surgery, strict vegan diet, and long-term metformin or PPI use. Folate deficiency arises from poor intake, alcoholism, pregnancy, and antifolate drugs. Distinguishing the two is essential because folate supplementation can mask but worsen B12-related neuropathy.
How each textbook covers it
Krause and Mahan's Food and the Nutrition Care Process, 16th ed. — Chapter 32
Hallmark findings: MCV >100 fL, hypersegmented neutrophils, elevated methylmalonic acid (B12 deficiency) or homocysteine (both B12 and folate deficiency). Causes of B12 deficiency include pernicious anemia, ileal disease, gastric surgery, strict vegan diet, and long-term metformin or PPI use. Folate deficiency arises from poor intake, alcoholism, pregnancy, and antifolate drugs. Distinguishing the two is essential because folate supplementation can mask but worsen B12-related neuropathy.
Modern Nutrition in Health and Disease, 12th ed. — Ch 97: Nutritional Anemias
Folate and B12 are required for thymidylate synthesis. Both produce indistinguishable hematology; distinguishing B12 (which also causes subacute combined degeneration) is critical because folate replacement can mask B12 deficiency while neurologic damage progresses. Other causes include methotrexate, hydroxyurea, and inborn errors of cobalamin metabolism. Workup: serum B12, methylmalonic acid, homocysteine, RBC folate, intrinsic factor antibodies.
Related terms
Cobalamin, Folate, MMA, Pernicious Anemia, Subacute combined degeneration, Vitamin B12